الفهرس 
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Abstract
The present study was planned to investigate the toxic effects of the orgnaophosphorus compound “metrifonate” in various concentrations for different periods of exposure on Oreochromus niloticus fish.
Clinical and pathological manifestations, alterations in blood cells, phagocytic activity and index and some serum biochemical constituents were used as a parameters for evaluation of the toxic effects.
Moreover, the withdrawal time needed for Metrifonate to removed from exposed fish was determined and all the parameters as in the acute and chronic exposure are done.
The effect of Metrif on the immunity of the exposed fish are evaluated through the determination of the antibody titer and mortality rate during the challenge trial.
The ability of Metrifonate to accumulate in fish flesh of toxicated fish were determined by gas chrornatographic method. This done for acute, chronic exposure and with drawl time determination.
The results achieved are summarized in the following points:
1. Lethal dose (LC50) assessment of Metrifonate in 0. niloticus was
0.33 mg/liter.
2. In the acute toxic exposure to Metrifonate doses by 0.25, 0.30 and
0.40 mg/liter for one week, respiratory manifestations loss of pigmentation to either dark or pale colour, protrusion of anal opening with haernotrhagic patches & some times ascitis with in erosions.
3. In the chronic toxic exposure to Metrifonate by dose 0. 17 mg/liter for 8 weeks, the more clear signs were darkness of fish colour with haernorrhagic patches & loosing of scales vat end of the trial the colour return to normal.